In general, in the medical field, an object is diagnosed by using the medical images obtained by a medical image diagnostic apparatus. Such a medical image diagnostic technique has become indispensable to current medical care, and a further improvement in diagnostic performance is desired.
Under the circumstances, for example, it is known that an X-ray computed tomography apparatus (to be written as an X-ray CT apparatus hereinafter) executes enlargement reconstruction (zooming-reconstruction) to improve the diagnostic performance. According to this enlargement reconstruction, a high-resolution image (an image with a high spatial resolution) is reconstructed upon limiting a reconstruction range to a portion of a scan range. Executing such enlargement reconstruction (zooming-reconstruction) makes it possible to obtain a high-resolution image corresponding to a reconstruction range, thereby improving the diagnostic performance.
When executing enlargement reconstruction in an X-ray CT apparatus, the operator must check the image (CT image) obtained by the X-ray CT apparatus, activate a function for reconstructing the image again (for example, a reconstruction retry function), and select projection data (raw data) necessary for the reconstruction. In addition, the operator must select an area as an enlargement reconstruction target (reconstruction range). With this operation, the apparatus executes enlargement reconstruction for the reconstruction range selected by the operator based on the projection data selected by the operator.
Note that the operator selects a reconstruction range by designating, for example, an enlargement ratio on an image, an enlargement center, and a reconstruction pitch representing the intervals between images in the slice direction.
As described above, when executing enlargement reconstruction, the operator needs to perform a plurality of operations. This is cumbersome for the operator.
In contrast to this, there is available a function of simply zooming (enlarging) (to be simply referred to as a zoom function hereinafter), for example, a medical image on a display screen. Using this zoom function makes it possible to easily change the enlargement position and the enlargement ratio (magnification) by using a mouse or the like. That is, the operator is only required to perform operations simpler than those required to perform the above enlargement reconstruction.
However, since a medical image is reconstructed at a low enlargement ratio by using the zoom function, even if the enlargement ratio is changed, the roughness of the medical image remains the same as that before the enlargement of the image. That is, the medical image enlarged by the zoom function is lower in diagnostic performance than the image for which the above enlargement reconstruction has been executed. In order to obtain high diagnostic performance, therefore, it is preferable to execute enlargement reconstruction.